The present invention relates to an optical pulse observing device and, more particularly, to an optical pulse observing device capable of permitting the clear, indirect observation of pulse laser light.
A laser beam has been used as a pointer and a level for a survey instrument because a laser beam expands scarcely and capable of highly rectilinear propagation. Helium-neon lasers, i.e., atomic gas lasers that emit a red light of 632.8 nm in wavelength were used as a light source of laser devices in earlier times. However, helium-neon lasers need a large oscillator and a high driving voltage of several thousands volts and are difficult to handle.
Recently, semiconductor lasers (hereinafter abbreviated to xe2x80x9cLD xe2x80x9d) capable of emitting red light similar to that which is emitted by helium-neon lasers have been developed and helium-neon lasers have been gradually replaced by LDs. Since LDs are easy to handle and can be powered by a battery, LDs have become used on many survey instruments.
Since laser light is radiant energy, there is a limit to an output power of a laser to ensure the safety of the eye. The output power limits for lasers are specified in minute steps for those that emit continuous laser light and those that emit pulse laser light. Output powers exceeding a safety limit are classified strictly.
Visible lasers generally employed in survey instruments are included in those of class 2 that are not required to be used under the control of a safety manager. Upper limit output power for visible lasers is 1 mW in the class 2. Although a visible laser included in a rotary laser device is graded class 2, the output of the visible laser in 0.25 s for which eyes are closed matters because of the rotation and hence the output power of the visible laser may be slightly higher.
However, since the absolute value of the power of the visible laser is small, it is difficult to recognize the laser light emitted by the visible laser visually in the sunshine in the daytime and the distance of visibility is very short. Such a problem may be solved by intermittent emission of laser light to utilize the visual sensitivity of eye. Actually, the visual recognition of the laser light emitted by the visible laser in the sunshine is very difficult.
Although the visibility of green laser light brighter than red laser light is somewhat higher than that of red laser light, it is still difficult to visually recognize green laser light in the sunshine. Thus the use of the visible lasers is limited to a guide beam for interior finish work or tunnels.
It is an object of the present invention to provide an optical pulse observing device that enables the clear observation of indirect light of pulse laser light and is to be used by a person for observing direct or indirect light of pulse illuminating light.
The optical pulse observing device according to the present invention includes an optical shutter means that operates for alternate opening and closing in synchronism with the periodic pulses of pulse illuminating light so as to open only during the duration of pulses of the pulse illuminating light to pass pulse illuminating light and external light.